This application is a 371 of PCT/EP92/00600 filed on Mar. 19, 1992.
The present invention relates, in general, to a circuit configuration for an electronic controller and, in particular, to a controller of a brake system having an electronic anti-locking control and/or traction slip control. This circuit configuration includes a monitoring circuit which, upon detection of a defective condition, malfunction, defective power supply or the like, will either maintain various actuator elements excited by the controller in their initial positions or restore various actuator elements excited by the controller to their initial positions. The actuator elements can be, for example, setting elements or magnetic valves of an electronically controlled brake system which are connected to a relay contact of a power supply relay that closes upon activation of the controller for supplying power to the actuator elements.
For safety reasons, brake systems that are provided with an electronic anti-locking control or traction slip control are designed such that, in a defective condition of the electronic control system or in the event of a power break-down, the magnetic valves of the brake system take a resting position, wherein the full brake effect--although uncontrolled--is ensured. The electronic system, as a consequence of malfunction or power break-down, must not be allowed to result in a failure of the brake system. To ensure this, the antilocking controller according to DE-PS 26 12 356 is equipped with a monitoring circuit which, upon occurrence of an error in the electronic control system, will deactivate the power supply relay. With the magnetic valves of the anti-locking controller also connected through the working contact of the relay, upon occurrence of such an error, the magnetic valves either remain in their resting position or are restored to their resting position. Pending removal of such error, only a conventional braking operation is possible, so as to ensure that the valves cannot exert an adverse influence on the brake function. The state-of-the-art monitoring circuit, for the most part, is in an intrinsically safe configuration so that the errors in both the electronic anti-locking control and in the monitoring circuit will result in deactivation of the power supply relay.
According to DE-OS 32 34 637, the continued operation of a conventional brake system, upon occurrence of a defective condition in the electronic system, is essentially ensured in the same manner, that is, by deactivating the power supply to the magnetic valves.
Moreover, DE-OS 39 24 988 teaches an actuator driven power supply relay comprising two series-connected transistors and a power supply relay which connects the magnetic valves of an anti-locking control system to the battery. A defective condition of one of the two transistors is detected by way of a test circuit, whereupon the power supply relay is deactivated.